The present invention relates generally to hydrocarbon production, and more particularly to compositions and methods useful for drilling a well bore in a subterranean formation.
A variety of drilling fluids are used in the drilling of oil and gas wells along with other drilling fluid applications and drilling procedures. In rotary drilling, drilling fluids perform a variety of functions and possess a variety of characteristics. Traditional drilling fluids include drilling muds, or simply “muds.” Drilling fluids are generally used to carry cuttings from beneath the drill bit, transport them through the annulus between the drill string and the well bore, and allow their separation at the surface while at the same time cooling and cleaning the drill bit. A drilling mud can also reduce friction between the drill string and the sides of the well bore while maintaining the stability of uncased sections of the borehole.
Typical drilling fluids can be classified according to their base fluid. Water-based muds comprise an aqueous fluid as the continuous phase. Solid particles can be suspended in an aqueous fluid, and in some cases, oil can be emulsified in the water. Similarly, brine-based drilling fluids are water-based muds in which the aqueous fluid is a brine. Oil-based muds (OBM) are the opposite in that an oleaginous fluid comprises the continuous phase. Solid particles can be suspended in oil, and in some cases, water or brine can be emulsified in the oil. The oil continuous phase typically includes, diesel, mineral oil, esters, or alpha-olefins.
Drilling fluids typically contain additives that are used for various purposes. One common additive is a fluid loss additive, which may be used to prevent the intrusion of drilling fluids into the subterranean formation being penetrated and to form a thin, low permeability filter cake which temporarily seals pores and other openings in the subterranean formation. A filter cake is the residue deposited on a permeable surface such as a subterranean formation surface when a slurry, suspoemulsion, or suspension, such as a drilling fluid, is forced against the surface under pressure. A filter cake is defined herein as a combination of any added solids, if any, and drilled solids with the drilling fluid. Filtrate is commonly understood to be the liquid that passes through the surface, leaving the filter cake on the surface. Reduced hydrocarbon production can result from reservoir damage when a poor filter cake allows deep filtrate invasion. In addition, a filter cake can be difficult to remove in some instances.
Thus, clean up of the formation after drilling into subterranean formations with drilling fluids such as water-based muds or OBMs can be an important step in preparing a well for production. Traditional techniques involve the use of one or more secondary fluids to remove or degrade the filter cake prior to producing the well or preparing the well for use as an injection well. As each treatment operation increases the complexity, and thus the cost, of drilling a well bore, more efficient filter cake and formation clean up is desired to maximize hydrocarbon recovery.